Control apparatus, communication system, communication method, and program

ABSTRACT

A control apparatus includes: a topology management unit that manages a network topology formed by including a plurality of relay apparatuses; a link aggregation group management unit that groups ports of the plurality of relay apparatuses, having a physical link with an arbitrary node of the network topology and manages the grouped ports as a port of a virtual logical link between the plurality of relay apparatuses and the arbitrary node; and a relay apparatus control unit that controls the plurality of relay apparatuses, having the grouped ports, so that, when one of the plurality of relay apparatuses receives a broadcast packet or a multicast packet, a plurality of same packet are not forwarded to the physical links that form the virtual logical link.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/376,835, filed Aug. 5, 2014, which is a National Stage Entry ofInternational Application No. PCT/JP2013/053079, filed Feb. 8, 2013,which is based upon and claims the benefit of priority of JapanesePatent Application No. 2012-026813 (filed on Feb. 10, 2012), thedisclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present invention relates to a control apparatus, a communicationsystem, a communication method, and a program. More specifically, theinvention relates to a control apparatus configured to performcentralized control over a relay apparatus, a communication systemincluding the control apparatus, a communication method, and a program.

BACKGROUND

In recent years, the technology called OpenFlow (OpenFlow) is proposed(refer to Non Patent Literatures 1 and 2). OpenFlow identifiescommunications as end-to-end flows, and performs path control, failurerecovery, load distribution, and optimization on a per-flow basis. AnOpenFlow switch specified in Non Patent Literature 2 includes a securechannel for communication with an OpenFlow controller. The OpenFlowswitch operates according to a flow table in which appropriate adding orrewriting is instructed by the OpenFlow controller. In the flow table, aset of a matching condition (Match condition) to be matched against apacket header, flow statistics information (Counters), and instructions(Instructions) defining processing content is defined for each flow(refer to section “4.1 Flow Table” in Non Patent Literature 2).

When the Open Flow switch receives a packet, for example, the OpenFlowswitch searches the flow table for an entry having a matching conditionthat matches header information of the received packet (refer to “4.3Match Fields” in Non Patent Literature 2). When the entry that matchesthe received packet is found as a result of the search, the OpenFlowswitch updates the flow statistics information (one or more Counters),and executes processing content (e.g., transmission of the packet from aspecified port, flooding of the packet, discarding of the packet, or thelike) described in the instruction field of the entry. On the otherhand, when the entry that matches the received packet is not found as aresult of the search, the OpenFlow switch transmits to the OpenFlowcontroller a request for setting the entry, or a request for determiningthe processing content of the received packet, through the securechannel. The OpenFlow switch receives the flow entry in which theprocessing content is defined, and then updates the flow table. In thismanner, the OpenFlow switch performs packet forwarding by using theentry stored in the flow table as a processing rule.

Patent Literature 1 discloses an invention in which physical portsbelonging to a link aggregation group are also to be managed by anOpenFlow controller. A user can thereby be made to arbitrarily controlthe physical port of an output destination, without depending on asorting algorithm or the like inside an apparatus including the physicalports belonging to the link aggregation group.

PATENT LITERATURE 1:

JP Patent Kokai Publication No. JP2011-160171A

NON-PATENT LITERATURE 1:

Nick McKeown and seven other authors, “OpenFlow: Enabling Innovation inCampus Networks,” [online], [Searched on Jan. 11, 2012], Internet <URL:http://www.openflow.org/documents/openflow-wp-latest.pdf>.

[NON-PATENT LITERATURE 2]

“OpenFlow Switch Specification,” Version 1.1.0 Implemented (WireProtocol 0x02), [online] [Searched on Jan. 11, 2012], Internet <URL:http://www.openflow.org/documents/openflow-spec-v1.1.0.pdf>.

SUMMARY

Each disclosure of the related art literatures is incorporated herein byreference. The following analysis is given by the present invention. Ina configuration where a link aggregation group is set on an OpenFlownetwork as in Patent Literature 1, however, there is a problem that,when a broadcast packet or a multicast packet flows into the OpenFlownetwork, the same packet is duplicately forwarded, depending on thebehavior of a node at each end of the link aggregation group, so thattraffic distribution cannot be performed according to a rule set for thelink aggregation group.

Therefore, there is a need in the art to efficiently forward a broadcastpacket and a multicast packet even in an environment where a linkaggregation group is set on a network of a centralized control typerepresented by OpenFlow.

According to a first aspect, there is provided a control apparatus,comprising: a topology management unit that manages a network topologyformed by including a plurality of relay apparatuses; a link aggregationgroup management unit that groups ports of the plurality of relayapparatuses, having a physical link with an arbitrary node of thenetwork topology, and manages the grouped ports as a port of a virtuallogical link between the plurality of relay apparatuses and thearbitrary node; and a relay apparatus control unit that controls theplurality of relay apparatuses, having the grouped ports, so that, whenone of the plurality of relay apparatuses receives a broadcast packet ora multicast packet, a plurality of same packets are not forwarded to thephysical links that form the virtual logical link.

According to a second aspect, there is provided a communication systemthat comprises: the above control apparatus; and a relay apparatus thatis controlled by the control apparatus.

According to a third aspect, there is provided a communication method bya control apparatus comprising a topology management unit that manages anetwork topology formed by including a plurality of relay apparatuses,the communication method comprising: grouping ports of the plurality ofrelay apparatuses, having a physical link with an arbitrary node of thenetwork topology, and managing the grouped ports as a port of a virtuallogical link between the plurality of relay apparatuses and thearbitrary node; and controlling the plurality of relay apparatuses,having the grouped ports, so that when one of the plurality of relayapparatuses receives a broadcast packet or a multicast packet, aplurality of same packets arc not forwarded to the physical links thatform the virtual logical link.

According to a fourth aspect, there is provided a program for a computerconstituting a control apparatus comprising a topology management unitthat manages a network topology formed by including a plurality of relayapparatuses, the program causing the computer to execute: grouping portsof the plurality of relay apparatuses, having a physical link with anarbitrary node of the network topology, and storing the grouped ports asa port of a virtual logical link between the plurality of relayapparatuses and the arbitrary node; and controlling the plurality ofrelay apparatuses, having the grouped ports, so that, when one of theplurality of relay apparatuses receives a broadcast packet or amulticast packet, a plurality of same packets are not forwarded to thephysical links that form the virtual logical link.

The present invention provides the following advantage, but notrestricted thereto. According to the present invention, even under anenvironment where a link aggregation group has been set on the networkof a centralized control type represented by OpenFlow, a broadcastpacket and a multicast packet can be efficiently forwarded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of a configuration of anexemplary embodiment of the present invention.

FIG. 2 is a diagram for explaining an example of an operation of theexemplary embodiment of the present invention.

FIG. 3 is a diagram showing an example of a configuration of a firstexemplary embodiment of the present invention.

FIG. 4 is a block diagram showing an example of a detailed configurationof a control apparatus in the first exemplary embodiment of the presentinvention.

FIG. 5 is a table showing an example of a topology table held in thecontrol apparatus in the first exemplary embodiment of the presentinvention.

FIG. 6 is a table showing an example of a LAG port management table heldin the control apparatus in the first exemplary embodiment of thepresent invention.

FIG. 7 is a table showing an example of a LAG terminal management tableheld in the control apparatus in the first exemplary embodiment of thepresent invention.

FIG. 8 is a flowchart showing an example of an operation (beforeregistration of a LAG) in the first exemplary embodiment of the presentinvention*

FIG. 9 shows an example of control information set in each relayapparatus (before LAG port formation) in the first exemplary embodimentof the present invention,

FIG. 10 is a flowchart showing an example of an operation (of a LAGregistration reception and path recomputation) in the first exemplaryembodiment of the present invention.

FIG. 11 is a diagram showing an example of computation of a broadcastpath that passes through a representative port.

FIG. 12 shows an example of control information set in each relayapparatus (after the LAG registration reception and the path recomputation) in the first exemplary embodiment of the present invention.

FIG. 13 is a flowchart showing an example of an operation (of settingLAG port control information) in the first exemplary embodiment of thepresent invention.

FIG. 14 shows an example of control information set in each relayapparatus (for preventing forwarding to any LAG port) in the firstexemplary embodiment of the present invention.

FIG. 15 shows an example of control information set in each relayapparatus (when receiving from one of LAG ports) in the first exemplaryembodiment of the present invention.

FIG. 16 is a flowchart showing an example of an operation (of resettingcontrol information when a LAG port failure has occurred) in the firstexemplary embodiment of the present invention.

PREFERRED MODES

In the present disclosure, there are various possible modes, whichinclude the following, but not restricted thereto. First, an overview ofan exemplary embodiment of the present invention will be described withreference to the drawings. In the following description, a referencesign in each drawing appended to this overview is appended to eachelement for convenience, as an example for help understanding, and doesnot intend to limit the present invention to the mode that has beenillustrated.

As shown in FIG. 1, the exemplary embodiment of the present inventioncan be implemented by a plurality of relay apparatuses 1102 to 1104configured to relay a packet between terminal apparatuses 1101, 1105,and 1106 and a control apparatus 1100A configured to control these relayapparatuses 1102 to 1104.

More specifically, the control apparatus 1100A comprises a topologymanagement unit 101 that manage a network topology formed by including aplurality of relay apparatuses 1102 to 1104; a link aggregation groupmanagement unit (LAG management unit) 102 that groups ports of theplurality of relay apparatuses, having a physical link with an arbitrarynode of the network topology, and manages the grouped ports as a virtuallogical link between the plurality of the relay apparatuses and thearbitrary node; and a relay apparatus control unit 103 that controls theplurality of relay apparatuses. The relay apparatus control unit 103controls the plurality of relay apparatuses, having the grouped ports,so that, when one of the plurality of relay apparatuses receives abroadcast packet or a multicast packet, a plurality of same packets arenot forwarded to the physical links that form the virtual logical link.

Assume that a link aggregation group (LAG) is formed by grouping portsof the relay apparatuses 1102 to 1104 connected to the terminalapparatus 1101 through physical links L1 to L3 as shown in FIG. 2, forexample. Then, the relay apparatus control unit 103 controls theplurality of relay apparatuses, each having a port among the groupedports, so that, when one of the relay apparatuses receives a broadcastpacket or a multicast packet, a plurality of same packets are notforwarded to a plurality of the physical links that form the virtuallogical link.

More specifically, the relay apparatus control unit 103 controls therelay apparatuses 1101 to 1103 so that the broadcast packet or themulticast packet is forwarded along a path including a predeterminedrepresentative one of the ports (link L3 using the representative portas an end point) and does not pass through the ports (end points of thelinks L1 and L2), which are not the representative port, as shown inarrowed lines in FIG. 2.

With the above-mentioned arrangement, the broadcast packet and themulticast packet can be efficiently forwarded even under an environmentwhere the link aggregation group has been set.

First Exemplary Embodiment

Next, a first exemplary embodiment of the present invention will bedescribed in detail with reference to the drawings. FIG. 3 is a diagramshowing an example of a configuration of the first exemplary embodimentof the present invention. Referring to FIG. 3, the configurationincluding terminal apparatuses 1101, 1105, and 1106, relay apparatuses1102, 1103, and 1104, and a control apparatus 1100 is shown. Theterminal apparatuses 1101, 1105, and 1106 are configured to performmutual communication through a network. The relay apparatuses 1102,1103, and 1104 are each configured to forward a packet transmitted fromeach of the terminal apparatuses as a communication path between therespective terminal apparatuses 1101, 1105, and 1106. The controlapparatus 1100 is configured to be connected to each of the relayapparatuses 1102, 1103, and 1104 through a control channel (indicated bya dashed line in FIG. 3) and controls the relay devices 1102, 1103, and1104. A reference sign 1108 in FIG. 3 represents a link aggregationgroup.

The relay apparatuses 1102, 1103, and 1104 can be formed by an OpenFlowswitch described in each of Non-Patent Documents 1 and 2, for example.Another switching apparatus capable of forwarding a packet based oncontrol information from the control apparatus 1100 can also be used.Each of reference signs P1 to P4 shown within boxes indicating the relayapparatuses 1102, 1103, and 1104 indicates a port number of each relayapparatus.

The terminal apparatuses 1101, 1105, and 1106 are a computer to beoperated by a user of the network, a server configured to provide aservice and content to these computers, or the like.

FIG. 4 is a block diagram showing a detailed configuration of thecontrol apparatus in the first exemplary embodiment of the presentinvention. Referring to FIG. 4, the configuration is shown whichincludes a relay apparatus communication unit 111, a topology generationunit 112, a topology table 113, a broadcast path computation unit (BCpath computation unit) 114, a broadcast path control unit (BC pathcontrol unit) 115, an address acquisition unit 116, a link aggregationgroup management unit (LAG management unit) 117, a link aggregationgroup port management table (LAG port management table) 118, and a linkaggregation group terminal management table (LAG terminal managementtable) 119.

The relay apparatus communication unit 111 transmits a control commandto each of the relay apparatuses 1102 to 1104 in response to a requestfrom the topology generation unit 112 or the BC path control unit 115.The relay apparatus communication unit 111 forwards a response from eachof the relay apparatuses 1102 to 1104 to the topology generation unit112 and the BC path control unit 115.

The topology generation unit 112 requests connection information of eachrelay apparatus to each of the relay apparatuses 1102 to 1104 throughthe relay apparatus communication unit 111, generates a network topologybased on a result of response of each of the relay apparatuses 1102 to1104, and then records the generated network topology in the topologytable 113. As a collection method of the connection information, amethod may be pointed out where a specific one of the relay apparatusesis made to transmit a packet for arrival confirmation to all ports, aresult of receiving the packet for arrival confirmation is stored ineach relay apparatus, and then the control apparatus 1100 reads theconnection information between the respective relay apparatuses, basedon the stored result of receiving the packet. Alternatively, a methodmay be employed where receipt of the packet for arrival confirmation isnotified to the control apparatus 1100 by each relay apparatus withoutstoring the result of receiving the packet for arrival confirmation inthe relay apparatus. As a typical protocol of this type, there is anLLDP (Link Layer Discovery Protocol). However, other protocols may beemployed. Alternatively, a method may be used where the topologygeneration unit 112 receives an input of topology information from theuser and registers the topology information in the topology table 113.

FIG. 5 shows an example of the topology table corresponding to thenetwork configuration in FIG. 3. Referring to FIG. 3, the port P1 of therelay apparatus 1102 is connected to the terminal apparatus 1101. Thus,referring to FIG. 5, an adjacent relay apparatus of the relay apparatus1102 and information on an adjacent port of the relay apparatus 1102 arcboth “None.” On the other hand, the port P2 of the relay apparatus 1102is connected to the relay apparatus 1104. Thus, referring to FIG. 5, theadjacent relay apparatus of 1104 and the adjacent port information of P2(indicating that the relay apparatus 1102 is opposed to the port P2 ofthe adjacent relay apparatus 1104) are obtained.

The BC path computation unit 114 computes a broadcast path starting fromeach of the terminal apparatuses 1101, 1105, and 1106, by referring tothe network topology registered in the topology table 113. As acomputation method of the broadcast path, a minimum spanning tree (ofwhich a Prim's algorithm and a Kruskal's algorithm are representative)or the like may be employed.

The BC path control unit 115 corresponds to the relay apparatus controlunit 103 in FIG. 1 mentioned above, generates control information forexecuting a packet forwarding along the broadcast path computed by theBC path computation unit 114, and sets the control information in therelay apparatuses 1102 to 1104 through the relay apparatus communicationunit 111. Even when the LAG port management table 118 or the LAGterminal management table 119 is updated, the BC path control unit 115performs control information resetting in view of the presence of theLAG and the representative port of the LAG, according to the procedurethat will be described later.

Though omitted in the description of this exemplary embodiment, the BCpath computation unit 114 and the BC path control unit 115 may compute aunicast path and may set control information for unicast in response toa request from each of the relay apparatuses 1102 to 1104 through therelay apparatus communication unit 111.

The address acquisition unit 1 16 extracts the transmission sourceaddress and the transmission destination address of the packet from therelay apparatus communication unit 111, and then outputs the extractedtransmission source and destination addresses to the LAG management unit117.

The LAG management unit 117 manages information for identifying the linkaggregation group (hereinafter referred to as “LAG identificationinformation”) and each terminal apparatus connected to the linkaggregation group, using the LAG port management table 118 and the LAGterminal management table 119. The LAG management unit 117 selects, fromamong the ports of the relay apparatuses of the LAG to which the LAGidentification information has been given (hereinafter referred to as“member ports”), one port representative of the member ports(hereinafter referred to as the “representative port”). Therepresentative port may be selected, using an appropriate algorithm inview of equalization of traffic at each member port and a link cost.

The LAG port management table 118 is a table for managing theconfiguration, which indicates LAG port information and so forth. FIG. 6shows an example of the LAG port management table 118. In the example inFIG. 6, the LAG using, as the member ports, the ports (ports PI of therelay apparatuses 1102 to 1104) of the relay apparatuses (e.g., therelay apparatuses 1102 to 1104 in FIG. 3) connected to a certain one ofthe terminal apparatuses (e.g., the terminal apparatus 110 1 in FIG. 3)is registered. The port P1 of the relay apparatus 1104 is selected asthe representative port of this LAG.

The LAG terminal management table 119 is a table for managing eachterminal connected to the LAG. FIG. 7 shows an example of the LAGterminal management table 119. In the example in FIG. 7, the MAC (MediaAccess Control) address of the terminal apparatus 1101 is associatedwith the LAG identification information of “1108” described above. Thiscorresponds to a state where the terminal apparatus 1101 is connected tothe LAG 1108.

Each unit (processing means) of the control apparatus 1100 shown in FIG.4 can also be implemented by a computer program that causes a computerwhich constitutes the control apparatus 1100 to execute each ofprocesses described above, using hardware of the computer.

Next, an example of an operation of this exemplary embodiment will bedescribed in detail with reference to the drawings. First, generation ofthe network topology and setting of the broadcast path by the controlapparatus 1100 (before registration of the LAG) will be described.

FIG. 8 is a flowchart showing an example of an operation of the firstexemplary embodiment (before registration of the LAG). Referring to FIG.8, the topology generation unit 112 first collects the connectioninformation between the respective relay apparatuses through the relayapparatus communication unit 111, thereby generating the networktopology (in step S001). The topology generation unit 112 records thegenerated topology in the topology table 113.

Next, the BC path computation unit 114 computes the broadcast path, byreferring to the topology table 113 (in step S002).

Next, the BC path control unit 115 generates the control information foreach of the relay apparatuses 1102 to 1104, according to a result ofcomputation of the broadcast path by the BC path computation unit 114(in step S003). It is assumed in this exemplary embodiment that a flowentry which associates match fields (Match Fields) to be checked againsta received packet and instructions (Instructions) configured to defineprocessing content is generated., as the control information.

Next, the BC path control unit 115 requests transmission of thegenerated control information to the relay apparatus communication unit111. The relay apparatus communication unit 111 that has received therequest sets the control information in the relay apparatuses (in stepS004). In this case, the BC path control unit 115 may set in each relayapparatus the control information for causing a specific one ofbroadcast packets to be forwarded to the control apparatus 1100. As thespecific one of the broadcast packets, an ARP (Address ResolutionProtocol) packet, or an LACP (Link Aggregation Control Protocol) packet,for example, may be pointed out. This allows recognition of eachterminal apparatus and execution of a negotiation with respect to linkaggregation.

FIG. 9 shows an example of the control information generated by the BCpath control unit 115. The first to third ones of the controlinformation from the top of FIG. 9 are set in the relay apparatus 1102.Similarly, the fourth to sixth ones of the control information from thetop of FIG. 9 are set in the relay apparatus 1103, and the seventh toninth ones of the control information from the top of FIG. 9 are set inthe relay apparatus 1104. When the relay apparatus 1102 receives abroadcast packet (hereinafter referred to as a “BC” packet) at the portP1, for example, the relay apparatus 1102 confirms that the BC packetmatches a Match condition (being a BC packet), and forwards the BCpacket to the ports P3 and P4. The BC packet transmitted from the portP4 of the relay apparatus 1102 arrives at the terminal apparatus 1105.On the other hand, the BC packet transmitted from the port P3 of therelay apparatus 1102 is received at the port P2 of the relay apparatus1103. When the relay apparatus 1103 receives the broadcast packet(hereinafter referred to the “BC packet”) at the port P2, the relayapparatus 1103 confirms that the BC packet matches a Match condition(being Any (not specified)), and forwards the BC packet to the ports P1and P3. Hereinafter, similarly, the BC packet arrives at every node.

Next, an operation of resetting (optimizing) control information afterthe link aggregation has been registered by the user will be described.

FIG. 10 is a flowchart showing an example of an operation (of receivingregistration of the LAG and recomputing a path) in the first exemplaryembodiment. Referring to FIG. 10, the LAG management unit 117 firstrecords in the LAG port management table 118 LAG configurationinformation (formed of the LAG identification information and memberport information) specified by the user (in step S101). It is hereinassumed that the LAG configuration information formed of the LAGidentification information of 1108 and the member port information of P1of (the relay apparatus) 1102, P1 of (the relay apparatus) 1103, and P1of (the relay apparatus) 1104 are recorded, as shown in FIG. 6.

Next, the LAG management unit 117 selects the representative port fromthe ports belonging to the same LAG, and records the representative portin the LAG port management table 118 in step S102). It is assumed hereinthat the port PI of (the relay apparatus) 1104 has been selected as therepresentative port.

Next, the BC path computation unit 114 computes a broadcast path, byreferring to the topology table 113 and the LAG port management table118 (in step S103). FIG. 11 is a diagram showing the broadcast path socomputed as to pass through the selected representative port.

Next, the BC path control unit 115 generates the control information forimplementing packet forwarding along the computed broadcast path (instep S104). In this case, the BC path control unit 115 excludes theports other than the representative port of the ports (member ports)belonging to the same LAG from a distribution destination.

Finally, the BC path control unit 115 requests the relay apparatuscommunication unit 111 to transmit the generated control information.The relay apparatus communication unit 111 that has received the requestsets the control information in the relay apparatuses (in step S105).

FIG. 12 shows an example of the control information generated by the BCpath control unit 115. The control information in FIG. 12 is differentfrom the control information shown in FIG. 9 in that when a BC packet isreceived at the member port P1, the packet is forwarded to the controlapparatus 1100 and that the ports P1 are deleted from the port of theforwarding destination (refer to broken-line circles in FIG. 12), whichis associated with the broadcast path in FIG. 11. Setting of thesecontrol information can also be implemented by requesting rewriting ofInstructions Fields of these control information when the controlinformation shown in FIG. 9 has already been set in each of the relayapparatuses 1102 to 1104.

In the example in FIG. 12, when the relay apparatus 1104 receives a BCpacket at the port P4, the relay apparatus 1102 confirms that the BCpacket matches a Match condition (being a BC packet), and then forwardsthe BC packet to the port P1 and the port P3. The BC packet transmittedfrom the port P1 of the relay apparatus 1104 arrives at the terminalapparatus 1101. On the other hand, the BC packet transmitted from theport P3 of the relay apparatus 1104 is received at the port P3 of therelay apparatus 1103. When the relay apparatus 1103 receives thebroadcast packet (hereinafter referred to as the “BC packet”) at theport P3, the relay apparatus 1103 confirms that the BC packet matches aMatch condition (being Any (not specified)), and forwards the BC packetto the port P2. Hereinafter, similarly, the BC packet arrives at everynode.

Next, a description will be given about an operation when a BC packet istransmitted from the terminal apparatus 1101 connected to the LAG in astate where the control information as mentioned above has been set.

When the BC packet is transmitted from the terminal apparatus 1101, theBC packet is received at one of the member ports P1 of the relayapparatuses 1102 to 1104 that form the LAG. The BC packet is thenforwarded to the control apparatus 1100 as shown in the controlinformation in FIG. 12 described above.

FIG. 13 is a flowchart showing an example of an operation of the controlapparatus 1100 (of setting LAG port control information) when a BCpacket is received from the terminal apparatus 1101 connected to theabove-mentioned LAG. Referring to FIG. 13, when the control apparatus1100 receives the BC packet, the address acquisition unit 116 obtainstransmission source address information from the received BC packet, andnotifies the transmission source address information to the LAGmanagement unit 117 together with information on the relay apparatus andthe port of the relay apparatus for the transmission source of the BCpacket (in step S201). It is assumed herein that the address informationof the terminal apparatus 1101 in FIG. 3 is obtained.

Next, the LAG management unit 117 checks whether or not the BC packethas been received at the port belonging to the LAG, by referring to theLAG port management table 118 (in step S202). Herein, when the BC packetis not received at the port belonging to the LAG, subsequent processesare omitted.

Next, the LAG management unit 117 associates and registers in the LAGterminal management table 119 the LAG identification information withthe address of the transmission source notified from the addressacquisition unit 116 (in step S203).

Further, the LAG management unit 117 requests the BC path control unit115 to generate the control information for processing the BC packetfrom the terminal apparatus connected to the LAG (in step S204). The BCpath control unit 115 that has received the request additionallygenerates the following two types of the control information.

A first one of the control information is control information(hereinafter referred to as “transmission source filtering BC”)configured not to forward to the representative port of the LAG a packetwith the address of the terminal apparatus (terminal apparatus 1101,herein) connected, to the LAG port as transfer source information, whenthe packet is received at the port of the relay apparatus to which therepresentative port of the same LAG belongs.

FIG. 14 shows an example of the control information (transmission sourcefiltering BC) to be generated by the BC path control unit 115. Adifference from the control information for the same port of a same oneof the relay apparatuses shown in FIG. 12 is that, as each Matchcondition, the MAC address of the relay apparatus 1101 (that can beobtained from the LAG terminal management table 119) is set, and thatthe port P1 is excluded from a forwarding destination. With thisarrangement, a BC packet transmitted from the terminal apparatus 1101 isnot forwarded to any one of the member ports, thereby avoiding a loop.

A second one of the control information is control information(hereinafter referred to as “transmission source permitting BC”)configured to cause packet forwarding to be performed along thebroadcast path when a BC packet using the MAC address of the terminalapparatus 1101 connected to the LAG as a transfer source is received atone of the member ports of the LAG.

FIG. 15 shows an example of the control information (transmission sourcepermitting BC) generated by the BC path control unit 115. With thisarrangement, a B C packet from the terminal apparatus 1101 connected tothe LAG is forwarded to a different one of the relay apparatuses or adifferent one of the terminal apparatuses.

A higher priority than the control information shown in FIG. 12 is givento each of the first control information in FIG. 14 and the secondcontrol information in FIG. 15. As a method of giving the priority,priority information may be given to each control information, orstorage positions of the first control information and the secondcontrol information may be instructed so that the first controlinformation and the second control information are searched at eachrelay apparatus earlier than the control information shown in FIG. 12.

Finally, the BC path control unit 115 requests the relay apparatuscommunication unit 111 to transmit the generated first and secondcontrol information (transmission source filtering BC and transmissionsource permitting BC). The relay apparatus communication unit 111 thathas received the request sets the control information in the relayapparatuses (in step S205).

By setting the first and second control information as described above,when each relay apparatus receives a BC packet, each relay apparatus canbe controlled not to flow the same BC packet into links that form theLAG.

According to the configuration of this exemplary embodiment, the samecontrol can be continued even if a failure has occurred at therepresentative port of a LAG. A detailed description will be given belowabout operations when the failure has occurred at the representativeport of the LAG, with reference to the drawing.

FIG. 16 is a flowchart showing an example of an operation of the controlapparatus 1100 (of resetting control information when the failure hasoccurred at the LAG port) when the failure has occurred at therepresentative port of the LAG. Referring to FIG. 16, the LAG managementunit 117 detects the failure at the representative port (in step S301).The failure of the representative port can be detected by collection ofthe connection information between the respective relay apparatuses bythe topology generation unit 112, notification from each terminalapparatus, or the like, for example.

Next, the LAG management unit 117 refers to the LAG port managementtable, selects a representative port from the member ports of the LAGwhere the failure has occurred at the representative port, and recordsthe representative port in the LAG port management table 118 (in stepS302).

Since the subsequent operations arc the same as the content describedwith reference to FIG. 10 (in steps S303 to S305). In this case as well,the procedure shown in FIG. 13 is performed to set first controlinformation and second control information (transmission sourcefiltering BC and transmission source permitting BC), if needed. Asdescribed above, the present invention achieves effects as will bedescribed below.

As described above, according to this exemplary embodiment, even underan environment where a LAG has been set on a network of a centralizedcontrol type represented by OpenFlow, a BC packet can be efficientlyforwarded. Further, traffic between a terminal apparatus and relayapparatuses connected to the LAG can also be finely distributed, usingthe above-mentioned algorithm of selecting a representative port.

Though the above description was directed to the exemplary embodiment ofthe present invention, the present invention is not limited to theabove-mentioned exemplary embodiment. Further variation, substitution,and adjustment can be added within the scope not departing from thebasic technical concept of the present invention. To take an example,the description of the above-mentioned exemplary embodiment was given,assuming that a broadcast packet is to be handled. The presentinvention, however, can be similarly applied to a multicast packet aswell.

The numbers of the control apparatus, the terminal apparatuses, and therelay apparatuses and the configuration of the network illustrated inthe above-mentioned exemplary embodiment are an example shown to helpunderstanding of the present invention. No particular limitation isimposed on the present invention. The present invention can also beapplied to a different network configuration capable of forming a LAG.

Each disclosure of the above-listed Patent Literature and Non PatentLiteratures is incorporated herein by reference. Modification andadjustment of each exemplary embodiment and each example are possiblewithin the scope of the overall disclosure (including the claims) of thepresent invention and based on the basic technical concept of thepresent invention. Various combinations and selections of variousdisclosed elements (including each clement in each claim, each elementin each exemplary embodiment and each example, each element in eachdrawing, and the like) are possible within the scope of the claims ofthe present invention. That is, the present invention naturally includesvarious variations and modifications that could be made by those skilledin the art according to the overall disclosure including the claims andthe technical concept.

-   P1-P4 port (number)-   101 topology management unit-   102, 117 link aggregation group management unit (LAG management    unit)-   103 relay apparatus control unit-   111 relay apparatus communication unit-   112 topology generation unit-   113 topology table-   114 broadcast path compulation unit (BC path computation unit)-   115 broadcast path control unit (BC path control unit)-   116 address acquisition unit-   118 link aggregation group port management table (LAG port    management table)-   119 link aggregation group terminal management table (LAG terminal    management table)-   1101, 1105, 1106 terminal apparatus-   1102, 1103, 1104 relay apparatus-   1100, 1100A control apparatus

1-10. (canceled)
 11. A control apparatus, comprising: a memory storing anetwork topology and a port group information of a plurality of switchapparatus; and a controller comprising a processor configured to executeprogram instructions to: determine, based on the port group information,a representative port from a plurality of ports belonging to a portgroup; calculate, based on the network topology and the port groupinformation, a flow path such that a predetermined packet passes onlythe representative port among the port group; determine, based on theflow path, a forwarding instruction to forward a packet along the flowpath; and send the forwarding instruction to the switch apparatus. 12.The control apparatus according to claim 11, wherein the predeterminedpacket is a multicast/broadcast packet.
 13. The control apparatusaccording to claim 12, wherein the predetermined packet includes asource address of the switch apparatus.
 14. The control apparatusaccording to claim 11, wherein the processor is configured to executefurther program instructions to store the port group informationregistered by user to the storage.
 15. The control apparatus accordingto claim 11, wherein the processor is configured to execute furtherprogram instructions to change the representative port when a failure ofthe representative port is detected.
 16. A communication system,comprising: a control apparatus; and a plurality of switches to forwardpackets based on forwarding instructions from a control apparatus,wherein the control apparatus comprises: a memory storing a networktopology and a port group information of a plurality of switchapparatus; and a controller comprising a processor configured to executeprogram instructions to: determine, based on the port group information,a representative port from a plurality of ports belonging to the portgroup; calculate, based on the network topology and the port groupinformation, a flow path such that a predetermined packet passes onlythe representative port among the port group; determine, based on theflow path, a forwarding instruction to forward a packet along the flowpath; and send the forwarding instruction to the switch apparatus. 17.The communication system according to claim 16, wherein thepredetermined packet is a multicast/broadcast packet.
 18. Thecommunication system according to claim 17, wherein the predeterminedpacket includes a source address of the switch apparatus.
 19. Thecommunication system according to claim 16, wherein the processor isconfigured to execute further program instructions to store the portgroup information registered by user to the storage.
 20. Thecommunication system according to claim 16, wherein the processor isconfigured to execute further program instructions to change therepresentative port when a failure of the representative port isdetected.
 21. A control method, comprising: determining, based on a portgroup information of a plurality of switch apparatus, a representativeport from a plurality of ports belonging to a port group; calculating,based on a network topology and the port group information, a flow pathsuch that a predetermined packet passes only the representative portamong the port group; determining, based on the flow path, a forwardinginstruction to forward a packet along the flow path; and sending theforwarding instruction to a switch apparatus of the plurality of switchapparatuses.
 22. The control method according to claim 21, wherein thepredetermined packet is a multicast/broadcast packet.
 23. The controlmethod according to claim 22, wherein the predetermined packet includesa source address of the switch apparatus.
 24. The control methodaccording to claim 21, further comprising: storing the port groupinformation registered by user to the storage.
 25. The control methodaccording to claim 21, further comprising: changing the representativeport when a failure of the representative port is detected.